ARC: BSP: Fix timer call-backs
ARC: BSP: Fix timer call-backs

In [1] we prefixed ARC Timer functions with "arc_"
and now we need to accommodate that change in RT-Thread
accordingly.

[1] https://github.com/foss-for-synopsys-dwc-arc-processors/embarc_bsp/commit/86a03d4bf99c8afad68c4c6a5941cda7a41dd4fe

RT-Thread/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread